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Controlled pressure drilling (CPD) has become the most effective drilling method to improve technical limit drilling time and reduce previously recorded lost time on offset conventionally drilled wells—when it is applied to correctly selected candidates. In addition, specific drilling techniques offered within CPD technology not only improve the time it takes to reach total depth (TD), but also have been proven to optimize reservoir section productivity and maximize economically recoverable reserves. CPD comprises three main techniques: air drilling, underbalanced drilling, and managed pressure drilling. This paper discusses the latest CPD techniques and the non-productive time that it can address. A methodology to properly screen all CPD techniques to reduce failure/misapplication and align objectives with expectations had been absent. This paper addresses the latest enhancements in an expert system developed to better understand and screen options for CPD operations. The Internet-based selection tool provides guidance by using key indicator questions, beginning with the primary objective(s) for the given wellbore section. If the specific CPD technique is known, the user can activate the online screening tool. The online screening tool considers a range of economic and technical parameters, as applied to algorithms and logic rules, to provide a relative ranking for each candidate of the CPD technique. Sensitivity analysis can also be performed to determine the impact of key uncertain parameters. Additional expert screening and selection methods are available upon the completion of the online CPD candidate selection process. The paper provides an overview of the Internet-based tool and methodology, in addition to supporting case histories. Introduction CPD is an adaptive drilling process that enables a more precise control of wellbore pressures through the use of engineered equipment and processes. The drilling process is becoming an important tool for drilling aging fields with depleted reservoirs, narrow pressure windows, and/or drilling issues. Drilling improvements stem from mitigating common drilling hazards that are caused by lost circulation, kick/loss scenarios, sour-gas influx, or simply slow drilling through hard formations; the end result is a reduction of avoidable cost. Loss of production and ultimate recovery result in an increase of the total cost per equivalent barrel of oil, reducing net present value (NPV). CPD effectively mitigates these issues, reducing non-productive time (NPT), improving productivity, as well as NPV, on both a well-to-well and field-to-field basis. The drilling process is defined by three major techniques:Air drilling (AD): Improve drilling economics by increasing rate of penetration (ROP) and extending bit life. Primarily applied in nonliquid hydrocarbon formations and the intent is to invite surface flow.Managed pressure drilling (MPD): Optimize drilling process by decreasing NPT and mitigating drilling hazards. The intent is not to invite surface flow.Underbalanced drilling (UBD): Increase reservoir productivity and maximize NPV by reducing formation damage and enhancing reservoir characterization. The intent is to invite surface flow. Fig. 1 provides more background on the individual techniques.

Until recently many of the wells on US land that were drilled using Managed Pressure Drilling (MPD) technology utilized one size fits all equipment designed for the offshore market. Since the cost and personnel requirements needed to run the offshore manifolds became a challenge due to market conditions and Covid-19 restrictions, the drillers sought a cost effective and simpler system to conduct their day-to- day operations. The challenge was to drill long laterals in Permian and Haynesville without losing the necessary MPD functionality that proved beneficial to reduce the risks associated with safety and to enhance drilling efficiency. For the MPD control system experts, the task was to correctly identify and automate MPD system’s functionality that would be of greatest use to the drillers to sustain their drilling performance. The concept of developing an easier to operate control system was undertaken wherein system accuracy and precision was maintained at the forefront of the development process. Electric motors/actuators and necessary drivers that could work directly on rig power were selected and tested. Control system logic that operates the chokes was modified to quickly adapt to the changes in drilling conditions, maintaining the necessary accuracy. This was done by studying and understanding drillers activities and behaviors like automated pump ramp down speed during connections, pipe movement during tripping etc. Specific MPD engineering charts, simple to decipher graphs, and necessary calculation tables were developed for the drillers to use for managing bottomhole pressures. Calculations which included specific schedules for spotting weighted pills were provided to maintain simplicity of the operations and something the drillers could easily execute. Today, many drillers are using this MPD solution to drill long laterals (Hovland et.al 2020). This trend is slowly leading to reduction of rig MPD personnel, especially during Covid-19, while the drillers are getting familiar with and operating MPD systems. A few of the crucial items that have allowed the drillers to run MPD on their own include MPD controls connected to drilling automation systems and the subsequent continuous revision of these controls based on understanding drillers tasks and needs. The use of electric motors enabled quick adoption to the changing drilling conditions while making connections, tripping etc. The furnished MPD calculations and graphs that drillers could follow for applying required MPD choke pressures kept MPD adaption simpler. The modifications made to the MPD choke controls geared towards facilitating necessary automation enabled the drillers to get trained in few days and operate the MPD systems while maintaining the same level of speed and performance.

Two hole sections (12-1/4Љ ϫ 14-3/4Љ and 10-5/8Љ ϫ 12-1/4Љ) were planned to be drilled through sequences of unstable shale and depleted sand packages with no drilling windows, which are defined by the shale Wellbore Stability Gradient (WBSG) delimited by the "intact wellbore wall zero failure degree" and the depleted sand fracture gradient criteria. Historically, significant non-productive time (NPT) associated with wellbore instability and lost circulation had resulted in sidetracks and other costly remediation in both hole sections. The operator and the service provider have identified the Constant Bottomhole Pressure (CBHP) variant of Managed Pressure Drilling (MPD) and wellbore strengthening as the necessary technology approach to safely drill through both challenging hole sections. Dynamic and static wellbore strengthening were applied to increase the near wellbore stresses across the depleted sands to create a drilling window, whilst the MPD CBHP was used to mitigate bottom hole pressure fluctuations and cyclic stress across the shale packages.The MPD well evaluated in this paper had just four hours of non-productive time related with downhole problems and wellbore stability, a minimal fraction when compared to the 980 hours lost in the previous conventional offset well. The MPD well did not require any back reaming operation, whereas the offset well in the area required 7 back-reaming events to get a good quality wellbore. A total of 533 hours were required to drill the 2 hole sections in MPD compared to the 2,410 hours required to drill the same sections conventionally in a previous offset well in the area. This paper summarizes the key MPD planning, engineering, results obtained and lessons learned that delivered a successful campaign of producer wells.